Frequency Hopping Datalink for GPS-Denied UAV Navigation
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Solution Overview
Problem
Current methods for autonomous aerial refueling, such as GPS and INS, are inadequate in GPS-denied scenarios due to position error accumulation and lack of precision, necessitating a reliable alternative for precise relative navigation between UAVs and tanker aircraft.
Innovation Solution
A frequency hopping communication system datalink utilizing an antenna array with at least three elements, which calculates ranging and bearing to determine accurate relative navigation, combining timestamp and phase differences to provide navigation solutions, and can be used as a backup to GPS or INS in GPS-denied environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS is used for position determination in aerial refueling, then navigation accuracy is improved, but the system becomes vulnerable to GPS jamming or blocking
Solution Approach 1:
The system changes the fundamental parameter of navigation from GPS satellite-based positioning to a ground-based or airborne beacons system using radio frequency signals. By transmitting known frequency dwells from a beacon and measuring time difference of arrival and phase differences at the aircraft, the system achieves positioning without relying on GPS satellites, thereby maintaining navigation accuracy while eliminating vulnerability to GPS jamming.
Solution Approach 2:
The patent introduces a beacon (ground-based or airborne) as an intermediary element between the aircraft and the navigation function. Instead of direct GPS satellite-to-aircraft communication, the beacon serves as a mediator that transmits timing and positioning signals to the aircraft, enabling the aircraft to determine its position relative to the beacon and tanker without direct GPS dependency.
2Reliability
If INS is used for position determination in GPS-denied scenarios, then the system maintains operation without GPS, but position error accumulates excessively after several minutes
Solution Approach 1:
The system implements feedback by continuously measuring the aircraft's position relative to a stationary or slowly moving beacon. The beacon provides reference signals that allow the aircraft to determine its actual position, and this information can be fed back to correct INS drift. The time difference of arrival and phase difference measurements provide continuous position updates that reset the error accumulation inherent in INS systems.
Solution Approach 2:
The patent merges INS with beacon-based navigation to create a hybrid system. The INS provides continuous position estimates and operates independently, while the beacon system provides periodic position corrections. By combining these two systems, the solution maintains the operational continuity of INS while eliminating its position error accumulation problem through periodic beacon-based updates.
3Reliability
If legacy systems like TACAN are used for navigation, then the system has established infrastructure, but the system lacks anti-jam robustness and has high detectability
Solution Approach 1:
The system uses periodic frequency hopping and time-diversity in signal transmission. The beacon transmits signals at different frequencies and times, and the aircraft measures position based on time difference of arrival across multiple frequency dwells. This periodic, distributed transmission approach makes the system more resistant to jamming compared to continuous single-frequency transmission, and reduces detectability by spreading the signal energy over time and frequency.
Solution Approach 2:
The system performs preliminary signal processing and measurement at the aircraft end using received beacon signals. By pre-calculating position based on time difference of arrival and phase differences before potential jamming occurs, and by using frequency hopping patterns that are difficult to predict or jam, the system achieves anti-jam robustness while maintaining infrastructure availability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate navigation solutions for UAVs and tanker aircraft, allowing for precise positioning and fueling operations even in GPS-denied conditions, with anti-jam robustness and low detectability, improving upon legacy systems like TACAN.
Implementation Method 1
The processing unit calculates a longitudinal phase difference based on the difference between the first frequency dwell received by the two longitudinal antennas and a lateral phase difference based on the difference between the second frequency dwell received by the two lateral antennas
Implementation Method 2
The UAV transmits a signal utilizing a frequency hopping communication system transmitter. The signal transmitted includes two short know frequency dwells
Data Source
AI summary
The present invention is directed to accurate GPS (global positioning system)-free relative navigation between an unmanned aerial vehicle (UAV) and a tanker aircraft. The UAV transmits a signal which is received by an antenna array at the tanker aircraft. Horizontal relative position of the UAV is determined by calculating range and bearing based on time and phase differences in the received signal. Vertical relative position of the UAV is determined by comparing the altitude of the UAV with the altitude of the tanker aircraft. The tanker aircraft then transmits a navigation solution based on the relative position of the UAV which is received by the UAV. The UAV may utilize the navigation solution transmitted by the tanker aircraft as a backup to a GPS determined navigation solution, in a GPS denied scenario, or in combination with an INS (inertial navigation system) determined navigation solution.